1. Field of the Invention
This invention relates to a method for forming channel stop diffusion layers, and more particularly to a method for forming channel stop diffusion layers formed on element separating areas in the manufacturing process of semiconductor devices.
2. Description of Related Art
As the semiconductor device has been densely integrated progressively, the element structure has been minimized. On the other hand, the on-chip system, which involves the combination of minimized semiconductor elements and systems for operating the semiconductor elements built on one chip, has been popular. In the case of on-chip semiconductor devices, low voltage elements with low voltage and high voltage elements with high voltage are formed on the same semiconductor substrate to accomplish minimization.
In a semiconductor device as described hereinabove, for example, the low voltage elements are separated individually by element separating films, and high voltage elements and channel stop diffusion layers formed under the element separating films are separated individually by the element separating films.
The channel stop diffusion layers are formed as described herein under.
At first, on a semiconductor substrate on which the element separating films are formed, a mask pattern comprising resist is formed. The mask pattern is a mask pattern for forming channel stop diffusion layers, openings are provided above the element separating films only in the high voltage sections.
Then, impurity is injected into the semiconductor substrate from above the mask pattern. Subsequently, the semiconductor substrate is heat-treated to diffuse the impurity into the semiconductor substrate, and channel stop diffusion layers are formed in the semiconductor substrate under the element separating films of the high voltage sections.
Channel stop diffusion layers may be formed before element separating films are formed on the surface of a semiconductor substrate.
The above mentioned channel stop forming method is involved in some problems as described herein under.
When impurity for channel stop is injected into a semiconductor substrate, a mask pattern for only the channel stop is formed on the semiconductor substrate, and impurity is injected from above the mask pattern. Consequently, the formation of channel stop diffusion layers requires complex processes comprising a process for forming the mask pattern, a process for injecting impurity into a semiconductor substrate, and a process for removing the mask pattern in addition to the regular manufacturing process.
This requirement is one of factors which make the manufacturing process complex for forming the semiconductor device.